Recently, automobiles that are equipped with airbags for saving the lives of occupants in automobile accidents are in widespread use. Moreover, as more advanced safety devices, side airbags and curtain airbags that cover nearly the entire side windows are installed in increasing numbers. These protect especially the heads of occupants during a side-impact vehicle crash. Such airbags are made from components obtained by impregnating specific woven fabric with a flexible resin. When installing such an airbag onto a vehicle body, an airbag is folded in a pleated manner, fastened with a fastener such as a thread or an adhesive tape, and placed such that the fastener breaks when the airbag goes off, so the airbag is instantly deployed.
As for the woven fabric that constitutes an airbag, fire-resistant woven fabric is normally used. This is to prevent a fire resulting from a high temperature inflation gas produced when deploying the airbag as well as the spread of vehicle fire. However, fire resistance was not a requirement of airbag fasteners. This was because the amount of fastener was extremely small relative to the entirety of a vehicle and to an airbag unit. However, as a result of an increased number of airbags installed per vehicle as airbags become widespread and automakers' increasing awareness of fire-resistant vehicle components, such a high level of fire resistance that, for example, FMVSS, 302 is satisfied is also required of airbag fasteners (e.g., adhesive tapes).
As an example of a method for imparting fire resistance to an adhesive tape, there is a method in which a flame retardant is added. However, such a method results in poor fastening properties, and accordingly a fastening tape may be separated during the period of handling from fastening of an airbag to installation onto a vehicle body or after equipping an automobile with an airbag.
To date, as an airbag fastener, an adhesive tape has been mainly used in which woven fabric obtained by plain-weaving acetate yarn, polyester yarn, acryl yarn, cotton yarn, or the like is used as a substrate. It has been believed more desirable to have a narrow adhesive tape width, or perform perforation processing on an adhesive tape if the adhesive tape has a large width, such that the adhesive tape instantly breaks when the airbag is deployed (see Patent Literature 1). However, when the adhesive tape has a narrow width, the substrate may unravel. Moreover, the perforation processing on the adhesive tape results in increased costs, which is age net cost reduction i.e., the priority of the auto industry.
In addition, in an adhesive tape that includes a woven fabric substrate, when an adhesive layer is thin or does not receive sufficient pressure during attachment, there is a possibility that the adhesive does not fill the irregularities of the back surface of the substrate, and the adhesive tape is separated. On the other hand, increasing the thickness of the adhesive layer to prevent separation increases material costs and requires a worker to perform a process of pressure bonding again on attached portions once an airbag is fastened, thereby resulting in increased costs.